Vascular grafts are currently used to augment or replace certain diseased arteries. Operations for this purpose are commonly done by surgeons who attach the graft to the side of the vessel proximal to the diseased region and again to the side of the vessel distal to the diseased region, thus bypassing the diseased region. Alternatively the graft is joined to the ends of the vessel remaining after removing the diseased portion. Clinically used artificial grafts have generally been restricted to vessel replacements requiring grafts of 6 mm and larger diameter, e.g., abdominal aorta, and lilac, femoral, and popliteal arteries. Natural vessels taken from other parts of the patients body, e.g., saphenous vein in the leg or internal mammary artery, are with few exceptions the choice for less than 6 mm diameter applications. Examples of the clinically used artificial vessels for arteries of large diameter are, for instance, DeBakey artificial vessel made of woven Dacron.RTM. (trademark of DuPont) and Gore-Tex.RTM. (Gore Co., Ltd., U.S.A.) which is made of expanded polytetrafiuoroethylene (hereinafter "EPTFE").
According to U.S. Pat. No. 4,834,746 the prior Dacron.RTM. and EPTFE graft materials have proven unsuitable at diameters of less than about 6 mm because of the compliance mismatch between the natural and artificial vessels. The proposed solution in U.S. Pat. No. 4,834,746 is to produce a vessel made of a microporous elastomer material. Elastomeric materials, however, lose wall thickness in the process of expansion and therefore eventually can result in aneurysm. Thus a conventional circular perimeter graft which merely utilizes an elastomeric material to provide a compliance match is not considered a fully satisfactory design.
Other variations in materials and configurations for vascular grafts are known, for example from U.S. Pat. Nos. 4,892,539; 4,605,406; 4,941,870; 4,759,757; 4,629,458; 4,300,224; and 4,647,416 as well as GB 2187463 and EP 0256748.
However, there still exists a need for improved vascular graft structure, particularly for graft structures which can be used at diameters below 6 mm.